1. Field of the Invention
The present invention generally relates to illumination using light emitting diodes (LEDs) and more particularly to brightness control circuitry for LED lighting apparatus.
2. Background of the Invention and Description of the Prior Art
There are a great many applications for light emitting diodes in apparatus intended for both signaling and illumination functions. Displays, lighting fixtures, signal lighting for vehicles and roadways, worklights for reading or performing close operations needing an intense, focused light source, portable lighting devices such as emergency lamps or flashlights, safety signaling products, are just a few such applications. Many of these application require the ability to control the beam geometry; other applications seek to control the brightness or illumination (light output in lumens) to provide the performance and variability required in given applications.
However, conventional circuits devised for controlling the light output from LED devices are too often complex, inefficient, expensive, insufficiently rugged, etc. for use in hand-held lighting devices such as flashlights used by public safety units—police, fire, the National Guard, etc.—where ruggedness, reliability, and uncomplicated control features are required. Complex circuits tend to be less reliable and more difficult to design to meet intrinsically safe standards. Some circuits employing switching regulators, which while efficient, may be susceptible to strong electromagnetic fields that may cause electromagnetic interference (EMI) when public safety personnel (police, fire, etc.) key their radio equipment while using their hand-held lighting devices. This situation, which may render hand-held lighting devices unsuitable because an expected mode of operation was impaired or even inoperative, is a completely inappropriate and potentially dangerous circumstance in a dark space that may place police or fire personnel at risk. What is needed is a circuit or apparatus for controlling LED lighting devices that are not susceptible to such problems.